The nerve cell membrane is assumed to be involved in many important developmental events. In the case of sensory ganglion neurons these may include migration from the neural crest, condensation into a ganglion, initiation of an axon, elongation of the axon, recognition and/or functional connection with the appropriate cells in the periphery. Axon outgrowth in vivo and in vitro shows a degree of specificity which implies that the neuron has the capacity to recognize and differentiate between cell surfaces or other factors in the environment. The hypothesis of this proposal is that proteins and/or glycoproteins in the neuronal plasma membrane mediate the specific recognitions made by developing neurons. It is also hypothesized that some of the neuronal pLasma membrane proteins change during development, as the neuron is confronted with new environments and new choices. The objective of the proposed research is to identify and characterize the protein and glycoprotein constituents of plasma membranes from chick embryo dorsal root ganglion neurons. Neurons will be separated from glial cells before plasma membrane preparations are made. Membranes from undifferentiated neurons will be compared to membranes from differentiated neurons of various developmental stages. The peptide structures of stage-specific membrane proteins will be characterized and antibodies to them will be made. Proteins in the plasma membrane of the growth cone region of the neuron will be compared to plasma membrane proteins from the cell soma and proximal axon. This work will increase our understanding of the nerve cell membrane and its function in developmental processes. It will form a basis for future work to determine what role specific membrane proteins play in directed axon outgrowth, and may lead to the development of new clinical treatments for developmental disorders of the nervous system.